Coalesced multifilament yarn



A. J. MEHLER, JR 3,342,027

COALESCED MULT I FILAMENT YARN Filed May 4, 1965 ALBERT JOSEPH ATTORNEY INVENTOR MEHLER JR.

United States Patent 3,342,027 COALESCED MULTIFILAMENT YARN Albert Joseph Mehler, Jr., New Hope, Va., assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware Filed May 4, 1965, Ser. No. 453,062 Claims. (Cl. 57140) This invention relates to composite textile yarns. More particularly, it relates to coalesced multifilament yarn, especially spandex yarn, possessing two levels of interfilament adhesion and to processes for obtaining such a product.

Smith Patent US. 3,094,374 describes a method for preparing coalesced spandex filaments during dry-spinning. The product produced by this process has good interfilament adhesion, but the method does not always give a coalesced yarn with an essentially round cross-section.

Accordingly, when yarns prepared by the Smith process are incorporated in hosiery in a laid-in construction, the lack of roundness of the yarn, which may be termed lack of cross-sectional uniformity, frequently produces appear= ance defects in the knit article.

This invention mitigates the effects of poor cross-sectional uniformity in coalesced yarn by providing a yarn which will partially separate into its components during textile processing. This invention also provides yarn with increased longitudinal denier uniformity.

These and other advantages are attained by a coalesced multifilament yarn comprising a plurality of individual groups of continuous filaments, said groups being joined together along their lengths but retaining their crosssectional identity, the average force required to separate said groups from each other being in the range from about 20 milligrams to about 50 milligrams, each of said groups comprising a plurality of individual continuous filaments similarly joined together along their lengths and retaining their cross-sectional identity, the average force required to separate said individual filaments from one another within the group being at least 45 milligrams and at least 1.5 times the average force required to separate said groups from each other.

In a preferred embodiment, the joining together of individual filaments within the groups and of the groups together is a result of self-bonding, i.e. of their own substance. Advantageously this is accomplished by heat coalescence during the yarn-forming process. According to this preferred embodiment, a solvent-containing solution of a thermoplastic fiber-forming polymer is extruded through a plurality of orifices into a spinning cell containing an evaporative medium to thereby produce separate filaments, the filaments are brought together while tacky into two or more separate groups to cause the individual filaments therein to adhere to one another at an adhesion level of at least 45 milligrams, the thusly formed separate groups are brought together while tacky to cause the groups to adhere to one another at an adhesion level which is from about 20 milligrams to about 50 milligrams but is no more than two-thirds the said filament adhesion level, and finally the composite yarn prodnot is withdrawn. The use of one or more jet twisters is highly advantageous to create the two different levels of adhesion in the composite yarn.

The invention will be further understood by reference to the drawings wherein FIGURES l and 2 are schematic illustrations of apparatus arrangements for carrying out the process of the invention.

Although the composite yarn of this invention may be produced with any of the conventional filament-forming substances, such as acrylonitrile polymers, cellulose acetate, nylon, etc., this invention is particularly useful in the making of coalesced spandex filaments. As is well known, the spandex fibers are elastic synthetic fibers in which at least 85% by weight of the fiber-forming substance is a segmented polyurethane. The segmented polyurethanes are well known in the art and are generally prepared from hydroxyl-terminated prepolymers, such as hydroxyl-terminated polyesters and polyethers of low molecular weight or mixtures thereof. Reaction of the prepolymer with a stoichiometric excess of diisocyanate produces an isocyanate-terminated material which may then be chain-extended with a compound containing active hydrogen, for example, water, hydrazine, organic diamines, glycols, amino alcohols, etc. Many segmented polyurethanes of this type are described in several patents. Among these are U.S. Patents 2,929,800, 2,929,804, 2,- 957,852 2,962,470, 2,999,839, 3,009,901, 3,071,557 and 3,097,192.

The yarns of this invention contain individual filaments which adhere to one another to form a unitary whole. There are two distinct levels of adhesion within the composite yarn. A primary level of adhesion exists between individual filaments to form a group of filaments. A secondary level of adhesion, lower than the primary level, exists between the groups of filaments which form the composite yarn. Although there are variations in the amount of adhesion at the primary level, it will generally be rather uniform within a group of filaments and should on the average exceed 45 milligrams of force, preferably exceed 60 milligrams of force. For the optimum practice of this invention, no more than 10% of the filaments within a group have a primary adhesion of less than 35 milligrams. The average primary adhesion must also be at least 1.5 times the average secondary adhesion and preferably is more than twice the secondary adhesion. For the most desirable yarns, the average primary adhesion falls Within the range from 4 to 6 times the secondary adhesion. Ordinarily, the primary adhesion does not exceed 250 milligrams. Otherwise, the group of filaments becomes almost indistinguishable from a true monofil. For the purposes of this invention, no more than 10% of the filaments within any group may have a primary adhesion in excess of 25 0 milligrams.

As explained above, the secondary adhesion between groups of filaments is much lower than the primary adhesion. Although there are variations in the amount of secondary adhesion, it should generally be rather uniform and should on the average be between 20 and 50 milligrams of force. If the secondary adhesion is too low, premature separation of the groups of filaments may occur and cause processing ditficulties, such as snagging during knitting. In general, such difliculties will be avoided if no more than 10% of the measurements of secondary adhesion in the composite yarn are less than 10 milligrams. Generally speaking, no more than 10% of the secondary adhesion measurements should exceed 70 milligrams.

As specified hereinabove, the average primary adhesion force must be at least 1.5 times the average secondary adhesion force and must amount to at least 45 milligrams. Thus, for secondary adhesion levels from 20 to 30 milligrams, the 45 milligram level is the minimum primary adhesion force required. For secondary adhesion levels from 30 to 50 milligrams, the primary adhesion must he at least 1.5 times the secondary adhesion figure, which requires a minimum primary adhesion of 45 to milligrams. For the best products, of course, a great difference between the primary and secondary adhesion levels is preferred. Thus, a primary adhesion which is 4 to 6 times the secondary adhesion is most desirable.

Each group of filaments within the composite yarn of this invention contains at least two individual filaments,

but more than two of such filaments are desirable. Preferably, the group of individual filaments will have a total denier of at least 20. The composite yarn contains at least two of the aforementioned groups and 'will preferably have a denier of at least 40. More than two groups in the composite yarn are desirable. Although the composite yarns may be of any size, composite yarns of about 100 denier or less are of the greatest interest.

The composite yarns of this invention may be prepared in various ways. In the preferred embodiment, the individual filaments are first coalesced to form groups and then the groups are brought into contact under less effective coalescence conditions. The groups are thus adhered to one another with the required lower level of secondary adhesion.

The dry-spinning process of the above-mentioned Smith patent can be used for producing a coalesced multi-filament spandex which can serve as a group of filaments. Thus groups of filaments produced by the Smith process are readily converted to the composite yarns of this invention by bringing them together at that stage in their formation when they are still sufiiciently tacky to adhere to one another and can provide adhesion levels within the 20 to 50 milligram range.

In one embodiment as shown in FIGURE 1, a spinning solution of suitable viscosity is pumped to a spinneret assembly mounted in the dry spinning cell 12. As the solution is extruded from orifices 13 in the spinneret, it

is met by a co-current stream of hot, inert gas introduced to the cell through inlet 14. The solvent of the spinning solution is evaporated into the hot, inert gas, thereby converting the several streams of spinning solution into continuous filaments 15 as they proceed down the cell. The filaments are combined into two groups 16 and 17. It is to be understood that the drawings have been simplified for purposes of illustration and that in practice a greater number of filaments and/ or filament groups would normally be extruded. A countercurrent stream of inert gas may also be introduced at the bottom of the cell through inlet 18 to minimize dripping of solvent from the cell. The two streams of inert gas meet and are drawn off through an aspiration device 20 near the bottom of the cell. The solvent may be recovered from the drawn-0E gas for reuse in the preparation of additional spinning solution.

Each filament group exits through a small hole 30' in the cell closure and passes through one of a pair of jet twisters 22 to stationary guide 25 and then to feed roll 28. The hole in the cell closure and the jet twisters are positioned with respect to the guide 25 such that the filaments pass from the spinneret to the guide without touching the cell closure or the walls of the jet. Thus, the only contact with a solid surface that the groups would have prior to reaching guide 25 is an occasional or accidental contact with the wall of the jet or the hole in the cell outlet.

The jet twisters 22 are each supplied with a steady flow of air through inlets 24. The action of each jet is such as to twist the filament group passing through it. The flow of air to the jet is adjusted so that this twist backs up into the cell to a point 27, which is the first point of filamentto-filament contact.

Within the cell 12, filament groups 16 and 17 individually achieve a primary level of adhesion as the tacky filaments coalesce in the vicinity of point 27. In the vicinity of stationary guide 25 the two groups 16 and 17 converge and coalesce to give the secondary level of adhesion. For some purposes a third twisting jet similar to jet 22 may be used in lieu of guide 25 to converge the filament groups 16 and 17. In any case, the temperature of the fibers in the groups as they reach guide 25 must be sufficiently high that the groups will join together. In some cases the air supplied to jet twisters 22 may have to be heated in order that the temperature of the fibers be not excessively reduced thereby.

Since the twist applied by the jet twisters is false twist,

the yarn leaves roll 28 essentially free of twist. It then passes over a finish roll 32 for application of a lubricant from reservoir 33, then to a second feed roll 34, and finally to a wind-up apparatus consisting of a traversing yarn guide 36, a drive roll 38, and bobbin 40. Roll 34 may be operated at a slightly lower, equal or slightly higher linear speed than roll 28, depending upon the denier, spinning speed, and spin-stretch ratio desired. The relative speed of these rolls is adjusted to overcome friction encountered while finish is being applied at roll 32. The composite yarn may be partially or completely relaxed between roll 34 and roll 38 to give the desired winding tension in the packaged yarn and to develop desirable physical properties in the final product.

The jet twister, as described in the aforementioned Smith patent, is of conventional design and consists essentially of a doughnut-shaped plenum chamber supplied with a tangential air inlet 24. The yarn passes through an orifice located at the center of the doughnut and is twisted by a swirling sheet of air issuing perpendicularly to the thread line.

FIGURE 2 illustrates an alternate and more simplified arrangement for forming the composite yarn of the invention, the same reference numerals being used therein to designate parts which are the same as those described above in connection with FIGURE 1. According to this embodiment separate jet-twisters 22 are not required to form distinct filament groups. In this case the spacing of orifices 13 in the face of the spinneret 10 is such as to form two or more filament groups. The various orifices are arranged in spaced clusters about the spinneret face, i.e. orifices within each cluster are spaced close to one another whereas the clusters themselves are spaced considerably farther apart. The distance between clusters should usually be at least twice the distance between individual orifices within any cluster. Upon being twisted by the jet 22, filaments from each cluster of orifices are brought together in the vicinity of point 27 and coalesce to form separate filament groups 16 and 17. Since the orifices of any cluster are relatively far apart from those of each other cluster, there is little or no tendency for filaments of one group to touch and coalesce with those of another group while in the spinning cell. Once outside the spinning cell, the filament groups, being of considerably reduced tackiness, converge at or just above jet 22 to give the secondary level of adhesion. The composite yarn so formed is then processed in the manner indicated above with reference to FIGURE 1.

Although the invention is described herein with particular reference to the attainment of two levels of adhesion in the composite yarn, it will be understood that in actual practice more than two levels can be provided so long as the values are within the above-specified ranges and the adhesion between groups is less than two-thirds that between fibers in the groups. For example in the arrangement of FIGURE 1, the position of one of the jets 22 can be raised or lowered relative to the other, alternatively the flow of air to that jet can be increased or decreased, such that the coalescence point 27 occurs for each group at a different distance from the orifices. In this case the primary adhesion level will still be in excess of 45 but will not be the same in both groups. When the groups are combined at guide 25, three different levels will occur in the composite yarn.

For the most part, primary coalescence of ordinary spandex yarns produced by a dry-spinning process is carried out where the fiber temperature is above 140 C., whereas secondary coalescence occurs best when the fiber temperature is less than about C. However, the composite yarns can also be produced by a wet-spinning operation and in this case if the spandex is sufiiciently plasticized, such as by retained water and/or solvent, primary coalescence may 'be achieved at temperatures above about 60 C. and secondary coalescence may be achieved at temperatures below about 50 C.

The formation of the composite yarn does not have to be carried out during the formation of the primary coalesced multifilament group. Thus, a suitable coalesced multifilament may be treated with plasticizer, or with solvent which acts as a plasticizer, such as by passage through a bath or over wicks, rollers, rods, or other devices moistened with the requisite quantity of appropriate liquid. The multifilament group is thereby rendered sufiiciently tacky so that when a plurality of such groups are brought together, as in a guide or slot, a composite yarn is formed. Preferably, however, the composite yarn is formed continuously with the extrusion and coalescence of the primary multifilament groups.

The levels of adhesion specified herein may be determined on a tensile testing instrument, such as the wellknown machine manufactured by Instron Engineering Corporation, Quincy, Mass. The level of secondary adhesion is determined by first selecting a suitable length of the composite yarn. If there are but two filament groups in the yarn, separation along the length is started manually and continued until the free ends are of sufiicient length that they may be placed in the clamps of the Instron machine. The clamps are then drawn apart at the rate of 5 cm. per minute, and the force required to continue the separation is determined. If there are more than two filament groups in the yarn, the length of yarn must be first subdivided for measuring the force required to separate each group from each of its neighbors to which it is adhered. For this purpose the composite yarn is subdivided into pairs of neighboring groups which are adhered to gether, the separation force measured for each pair in in the manner described above, and the values average for the pairs so measured. It will be apparent that the separation force for each pair should itself be anaverage value obtained by measurements at intervals along the pair. The primary adhesion level is made in the same manner except that a single group is subdivided and used for measurement of the average force to separate indi' vidual filaments from one another;

. Although the composite yarns of this invention are not visibly different from the ordinary coalesced multifilament spandex of equivalent denier, they will separate into groups of filaments under the stresses of knitting. Better appearing hosiery is thereby produced, particularly in the case of hosiery containing laid-in spandex yarn. The separation of the composite yarn has the effect of eliminating the unsightly flashes in the hosiery usually caused by the concentrated appearance of ordinary coalesced spandex. Thus, the improvement in appearance results from an over-all gain in cross-sectionsymmetry and a randomization of the remaining variations.

. A'coalesced spandex yarn having two levels of adhesion within its structure is also advantageous in other knitted or woven textile fabrics. For example, power-net fabrics made from bare spandex coalesced in the ordinary way frequently show pin holes in regions of variable density which are caused by varying orientations of the ribbonlike spandex. As in the case of the hosiery, these fabrics have improved appearance when made with spandex yarn having two levels of adhesion. Another advantage of this invention, which is observable in some cases, is that the instant composite yarns have increased longitudinal denier uniformity; that is, variations in denier along the length of the yarn are reduced. Since the sources of poor longitudinal denier-uniformity are frequently mechanical to a great extent, for example as arising from pulses in the spinning solution pumps, speed variations in the windup roll, etc., it is quite surprising that a composite filament of such yarns would have the longitudinal variations out of phase and thus tend to be more uniform in denier.

This invention is further illustrated, but is not intended to be limited, by the following examples in which parts and percentages are by weight unless otherwise indicated. The denier variability is measured by passing the fiber through a capacitance gauge such as in the Uster Evenness Tester. The instrument generates a signal which is a function of the mass of material in the gauge. The continuous signal from the gauge is fed to an integrator from which the root-mean-square deviation from the average denier of the sample is read as percentage of the average denier.

In the examples the spandex yarns are made up into support-type hosiery by circular knitting on a Scott & Williams AMF full-fashioned hosiery machine. In the laid-in constructions, the spandex is passed through the nylon stitches without being knit into the stitch. In the knit-in constructions, alternate courses of nylon and spandex are knit together in each stitch. The laid-in hosiery is made by knitting 30-denier nylon at 45 inche per course, the spandex being laid into the nylon under sufficient tension to give a course length of 12 /2 inches. On removal from the knitting machine, the hose have 40 stitches per inch. The knit-in hosiery is made by knitting alternate courses of 40-denier nylon (38 /2 inches per course) and 70-denier spandex (13% inches per course), 20-denier nylon being laid-in at a length 23 /2 inches per course. On removal from the knitting machine, the hose have 88 stitches per inch. Scouring, dyeing, and boarding operations are performed on each type of hosiery accord ing to ordinary commercial procedures.

Example I This example demonstrates the simultaneous production of eight individual yarns from a single spinning cell. Each of the eight yarns is composed of two groups of fibers, each of the groups being composed of three filaments. The apparatus employed is similar to that illustrated in FIGURE 2.

A spandex polymer solution in dimethylacetamide is prepared by the reaction of polytetramethyleneether glycol of molecular weight about 2,000, p,p'-methylenediphenyl diisocyanate, and m-xylylenediamine in the usual way. This spinning solution containing about 37% solids by weight is heated to a temperature of 60 C. and extruded through a spinneret containing 48 holes each 0.007 inch (.178 mm.) in diameter. The holes are arranged in clusters of three, each hole spaced 0.25 inch (6.25 mm.) from the neighboring holes in the group. Each cluster of three holes is spaced 1.05 inches (26.4 mm.) from adjacent groups of holes. After passing through a vertical spinning 'cell, which is supplied with a cocurrent stream of Kemp gas heated to 345 C. the filaments from neighboring pairs of three-hole groups are passed through one of a series of eight vortex jet twisters, each having an open stringup slot as described in copending application of Clendening, S.N. 403,486, filed Oct. 13, 1964. Air is supplied to the jet twister at about 075 cubic foot (21,000 cc.) per hour, whereby the torque developed is sufficient to twist each group of three individual filaments together at a point about 6.6 feet (2 meters) above the jet, which point is in the spinning cell. The torque also twists the two groups of filaments together, but this twist extends only for a distance of about 23 inches (5 cm.) above the jet. This latter point is well outside the spinning cell. After passing through the jet twister, the eight separate composite filaments, each of about 70 denier, are treated with finish and are Wound up as described in the aforementioned Smith patent.

The composite yarns so obtained are measured for interfilament adhesion on the Instron Tester as described hereinbefore. The individual yarns are found to consist of two groups, 35-denier each, of coalesced filaments. The two groups adhere to each other with an average force of 30 mg. The adhesion of the filaments within each group is 60 mg. A composite yarn of this example is found to have a denier variability of 1.5% as compared to 2.9% for a control yarn produced under otherwise identical conditions but to have only a single level of adhesion.

Laid-in hosiery containing the spandex yarn produced to have a double level of adhesion appears to be essentially free from flashes and streaks. Knit-in hosiery containing this spandex yarn is essentially free from the appearance of rings and bands which are found in knitin hosiery made from the control spandex.

Example H The spinning solution of Example I is extruded under the same conditions except that each group consists of four individual filaments. The secondary adhesion is 30 mg. The primary adhesion is 60 mg. Knit-in and laid-in hosiery show superiority in appearance over the controls, as was found in Example 1. Longitudinal denier variability is 1.2% as compared to 2.6% for the control.

Example 111 The spinning solution of Example I is extruded as described therein except that the diameter of the spinneret holes is 0.012 inch (0.3 mm.) and the flow of air to the jet twister is 1.0 cubic foot (28,000 cc.) per hour. The secondary adhesion between the two groups of filaments in the composite yarn averages 40 mg. The primary adhesion between filaments within each group averages 230 mg. Laid-in and knitin hosiery are superior in appearance to hosiery from control spandex yarns. Denier variability is 1.7%, as compared to 2.9% for the control.

Example IV The spinning solution of Example I is extruded as described therein except the apparatus is similar to FIG- URE 1 in that each group of three filaments is passed separately through a jet twister supplied with air at 1.2 cubic feet (34,000 cc.) per hour. The two groups of filaments are then combined by passing through a common guide placed just ahead of the finish roll. The composite spandex yarn of 70 denier has an average secondary adhesion of 36 mg. and a primary adhesion of 160 mg. Laid-in and knit-in hosiery are superior in appearance to the controls. Denier variability is 1.5%, as com pared to 2.9% for the control.

Example V The spinning solution of Example I is extruded as described therein except that each group consists of 9 filaments. The composite yarn of 70 denier has primary and secondary adhesion forces of the same order as those in Example I. Denier variability is 1.6%, as compared to 2.7% for the control.

Example VI The spinning solution of Example IV is extruded as described therein except that each group consists of four filaments, which are coalesced in separate jet twisters after which three adjacent groups of filaments are brought together in another jet twister for coalescence to form the final composite yarn. This yarn of 70 denier has primary and secondary adhesion forces of the same order as those in Example I. Denier variability is 1.1%, as compared to 2.5% for the control. Knit-in and laid-in hosiery are superior in appearance to the control fabrics.

What is claimed is:

1. A coalesced multifilament yarn comprising a plurality of individual groups of continuous filaments, said groups being joined together along their lengths but retaining their cross-sectional identity, the average force required to separate said groups from each other being in the range from about 20 milligrams to about 50 milligrams, each of said groups comprising a plurality of individual continuous filaments similarly joined together along their lengths and retaining their cross-sectional identity, the average force required to separate said individual filaments from one another within the group being at least 45 milligrams and at least 1.5 times the average force required to separate said groups from each other.

2. A coalesced multifilament yarn according to claim 1 wherein individual filaments are joined together by their own substance within the groups and wherein, similarly, the individual groups are joined together by their own substance within the yarn.

3. A coalesced multifilament yarn according to claim 1 wherein the filaments are elastic synthetic fibers in which at least 85% by weight of the fiber-forming substance is a segmented polyurethane.

4. A coalesced multifilament yarn according to claim 1 wherein the filaments are dry-spun spandex filaments.

5. A coalesced multifilament yarn according to claim 1 wherein the average force required to separate individual continuous filaments from one another is in the range of 45 to 250 milligrams.

6. A coalesced multifilament yarn according to claim 1 wherein the average force required to separate individual continuous filaments from one another is in the range of 45 to 250 milligrams, no more than 10% of the filaments within any group having a separation force below 35 milligrams and no more than 10% of the filaments within any group having a separation force above 250 milligrams.

7. A coalesced multifilament yarn according to claim 1 wherein the average force required to separate individual continuous filaments from one another is in the range of 60 to 250 milligrams, and is at least twice the average force required to separate said groups from each other.

8. A coalesced multifilament yarn according to claim 1 wherein the average force required to separate said individual groups from one another is in the range from about 20 milligrams to about 50 milligrams, no more than 10% of the groups in the yarn having a separation force below 10 milligrams and no more than 10% of the groups in the yarn having a separation force above milligrams.

9. A coalesced multifilament yarn according to claim 1 having a denier of up to about 100.

10. A knit fabric comprising the coalesced multifilament yarn defined in claim 1.

References Cited UNITED STATES PATENTS 3,094,374 6/ 1963 Smith 264103 3,161,706 12/1964 Peters 264103 STANLEY N. GILREATH, Primary Examiner.

J P R K l i z nt Examine 

1. A COALESCED MULTIFILAMENT YARN COMPRISING A PLURALITY OF INDIVIDUAL GROUPS OF CONTINUOUS FILAMENTS, SAID GROUPS BEING JOINED TOGETHER ALONG THEIR LENGTHS BUT RETAINING THEIR CROSS-SECTIONAL IDENTITY, THE AVERAGE FORCE REQUIRED TO SEPARATE SAID GROUPS FROM EACH OTHER BEING IN THE RANGE FROM ABOUT 20 MILLIGRAMS TO ABOUT 50 MILLIGRAMS, EACH OF SAID GROUPS COMPRISING A PLURALITY OF INDIVIDUAL CONTINUOUS FILAMENTS SIMILARLY JOINED TOGETHER ALONG THEIR LENGTHS AND RETAINING THEIR CROSS-SECTIONAL IDENTITY, THE AVERAGE FORCE REQUIRED TO SEPARATE SAID INDIVIDUAL FILAMENTS FROM ONE ANOTHER WITHIN THE GROUP BEING AT LEAST 45 MILLIGRAMS AND AT LEAST 1.5 TIMES THE AVERAGE FORCE REQUIRED TO SEPARATE SAID GROUPS FROM EACH OTHER. 